This invention relates to a push button switch, particularly a master, or power, switch, of a type having contacts attached to a housing and at least one movable contact bridge which is moved by a spring plunger, there being a spring switching mechanism transmitting force between the spring plunger and a manually-manipulated switch actuator, the push button switch also including a latching, or locking, linkage for the switch actuator for alternately locking the switch actuator in "on" and "off" positions.
Such switches are used for controlling power to electrical entertainment appliances, particularly television-type appliances.
German Patent Publication DE-AS 1 590 503 discloses such a push button switch. Experience has shown that such push button switches, despite their over-center spring switching mechanisms, can be undesirably manipulated by means of their switch actuators so that contact pressures are thereby influenced. When the switch actuators of such push button switches are not manipulated quickly enough, that is they are operated very slowly and/or only partially, it can happen, in spite of the over-center spring switching mechanism, that a contact pressure with which a contact bridge presses against housing-affixed contacts will go to zero and that this condition can be manually maintained. This causes an increase in contact resistance and, consequently, contact heating. Contact erosion is also coupled to this. Further, an overheated push button switch can result whose functioning ability as well as life span is not only decreased but which also presents a fire hazard.
A similar push button switch is disclosed in German Publication DE-GM 91 01 126. The system described herein is supposed to reduce contact bounce. However, this switch also has the above mentioned problems.
German Patent Publication DE 31 50 046 A1 discloses a push switch in which partially fused contacts are supposedly ripped apart by a separating mechanism. This system does not eliminate the above mentioned problems.
Another push button snapping switch is disclosed in German Patent Publication DE 28 39 108 A1. In this system a switch actuator must be pushed in opposite directions to turn the switch off and on. In the switch of German patent Publication DE 28 39 108 A1 arcing and contact bounce are supposedly reduced. To accomplish this a latching, or locking, apparatus is provided which blocks a spring plunger in its two end positions, with the spring plunger then being releasable by movement of a switch actuator. Also in this switch undesired manipulations are possible which cause the above mentioned problems to appear.
A further push button switch is disclosed in German Publication DE 20 31 364 A1. Also in this system the switch actuator is not latched alternately with each depression thereof between the "on" and "off" positions. In order to achieve a snapping action a member coupled to a snapping spring is shoved over a cam.
In German Patent Publication DE 36 44 437 C1 a push button switch is disclosed having a rocker arm and a rocker-arm engaging locking finger, which form locking linkage parts. One of the locking linkage parts is yieldably held by a spring in order to accommodate an overloading of its manipulation member in the manipulation direction.
A push button switch is described in German Patent Publication DE 43 01 192 C1 (U.S. Pat. No. 5,360,954) in which a manual manipulation leads to little increased erosion and operation dependability. A rubbing surface pair between a spring plunger and a housing mounted member, leads, shortly before a snapping of a spring switching mechanism caused by shoving a switch actuator, to an increased rubbing between the spring plunger and the housing mounted part whereby the snapping of the spring plunger is delayed.
The spring of the spring switching mechanism passes through its fully tensioned point when the switch actuator is moved. If the spring plunger begins to move it will be braked by the rubbing surface pair before the snapping point is reached so that a necessary contact pressure is maintained. The snapping point is, thereby, first reached at a greater spring tension than without this desired delay of movement of the spring plunger before the snapping; the spring plunger thereby passes through the snapping point also faster. In this manner, the snapping point, and therefore a contact pressure, can hardly be influenced by an improper manipulation of the switch actuator. The danger is also not present that the switch actuator can be manipulated and/or blocked in positions in which an increased contact transition resistance or electrical arcs lead to overheating, and thereby to increased erosion or fire hazards. A further rubbing surface pair between the spring plunger and a part affixed to the housing brakes movement of the spring plunger before impact of a contact bridge with housing-mounted contacts whereby bounce of the contacts is reduced.
It is an object of this invention to provide a push button switch that provides an improved switching operation, particularly when contact is made.